DESCRIPTION (provided by investigator): Human metapneumovirus (hMPV) is a newly described viral pathogen of acute respiratory infection (ARI). There are no descriptions of the role of hMPV in India or any other developing country. The proposed work will test the hypothesis that hMPV is an important contributor to the burden of ARI in India. India has 2.5 million deaths per year among children less than 5 years of age. ARI causes as many as 0.5 million of these deaths. The proposed studies are exploratory as there are no data on the contribution of hMPV to ARI in India. Support for these investigations will develop capacity for the study of hMPV in the second most populous country in the world. Aim 1. Determine the proportion of ARI associated with hMPV in a developing country, India. Children with ARI and ALRI seen in a large urban teaching hospital in New Delhi will be enrolled in the study. The clinical spectrum of disease will be described. Nasopharyngeal samples will be tested for the presence of hMPV by RT-PCR and cell culture. Aim 2. Develop techniques for molecular detection and genetic characterization of hMPV from India. Real-time RT-PCR detection will be used to improve the sensitivity of detection of hMPV. Nucleotide sequences for regions of the N, F, and G genes of hMPV will be determined and compared among Indian hMPV and viruses from other countries. These data for will help define the global epidemiology of hMPV and provide critical information relevant to hMPV diagnostic assay and vaccine development for India. Aim 3. Determine the prevalence of antibodies to hMPV among different age groups at a large urban teaching hospital in India. No data are available as to prevalence of antibodies to hPMV in developing countries. Assays for detection of hMPV antibodies will be developed and seroprevalence defined.